This invention relates to a stabilized zeolite Y with a very low unit cell constant (a.sub.o) made by a process involving the dealumination of zeolite Y and subsequent steps involving aluminum ion exchange, calcination, and acid treatment. In particular the zeolite Y product has an a.sub.o of less than 24.14 .ANG.. Such low a.sub.o values are realized by imposing a previously unknown control on the dealumination and stabilization process.
Various forms of stabilized zeolite Y are used as supports for hydrocarbon conversion catalysts. Stabilized zeolite Y is formed by removing some of the alumina from the zeolite crystal structure (dealumination) through various hydrothermal and chemical processes. Dealumination is accompanied by shrinkage of the a.sub.o and removal of sodium.
A review of various dealumination methods and descriptions of the products produced is provided by Sherzer, "Catalysts Materials: Relationship Between Structure and Reactivity," ACS Symposium Series, ed. T. E. Whyte, Jr., et al, 248, 151 (1984). This reference shows highly dealuminated Y zeolites with a.sub.o values of 24.25 .ANG..
Dealuminated Y zeolites can be further treated by ion exchange with aluminum ions followed by steam calcination. International Patent Application PCT/SE87/0044 (International Publication Number: WO 89/003367) teaches such a method that results in zeolite Y materials with a.sub.o values as low as 24.15 .ANG..
It is an object of this invention to control the method of dealumination and stabilization of zeolite Y so that materials with a.sub.o values of 24.14 .ANG. or less can be prepared.